Not only did Bosch invent the Electronic Stabilization Program (ESP) – the technology that improves a vehicle's stability by detecting / reducing loss of traction – but it also was the first company to fit Anti-locking Braking Systems (ABS) into mass production. The ABS system applies brake fluid that engages the brake calipers and pads, which slows a car without locking up the tires. The wheel speed sensor transmits the wheel speed to the ECU (Electronic Control Module), which determines how much pressure the ABS system can safely apply. Bosch is an original equipment global leader in wheel speed sensor technology. Bosch Wheel Speed Sensors ensure accurate information about the wheels' rotation characteristics are delivered to the ABS/ESP control unit. Sold individually.